Slot conductor for dynamoelectric machines



March 29, 1955 L. WAGENSEIL 2,705,292

SLOT CONDUCTOR FOR DYNAMOELECTRIC MACHINES Filed May 6, 1954 INVENTOR. .Ludwig Wugenseill ATTORNEY United States Patent "ice- SLOT CONDUCTOR FOR DYNAMOELECTRIC MACHINES Ludwig Wagenseil, Berlin-Siemeusstadt, Germany, as-

signor to Siemens-Schuckertwerke Aktiengesellschaft, Berlin-Siemensstadt, Germany, a corporation of Germany Application May 6, 1954, Serial No. 428,073

Claims priority, application Germany May 7, 1953 9 Claims. (Cl. 310-196) My invention relates to insulated conductors and is directed particularly to improved insulated conductors for slot windings in dynamoelectric machines.

In dynamoelectric machines whose slot conductors operate at a higher potential than the iron core in which the slots are formed, the entire slot-traversing conductor, composed of a plurality of individual conductors, is as a rule surrounded by an insulating sleeve or jacket. This jacket is usually produced by winding upon the conductor a sufiicient number of layers of mica paper, such paper having scales or foils of mica attached by means of shellac, and thereafter solidifying the mica-coated paper by the application of heat and pressure to form a rigid sleeve. The conductor thus insulated is then placed into the slots. Such insulated winding elements or rods are preferably of rectangular over-all cross section and consist in most cases of a plurality of individual conductors twisted so that each conductor occupies a varying position from top to bottom in the slot to minimize detrimental effects of non-uniform distribution of current density.

It has been found that in ordinary insulated conductors manufactured as described above, it is impossible to place the insulating sleeve into snug contact with the exterior surface of the slot conductor at all points. There always remain a number of air-filled hollow spaces along the faces of the slot conductor. An electric field, caused by the potential difference between the slot conductors and the slot wall, is therefore present not only in the interior of the insulating sleeve but also in the interior air spaces between the conductors and the inside wall of the insulating sleeve. The occurrence of glow discharges within these air spaces is inevitable at the high electric field strengths ordinarily surrounding these conductors. Such discharges greatly reduce the useful life of the slot conductor and its insulation.

To prevent vibrations, the individual conductors of the slot conductor according to common practice are firmly joined with each other. This is ordinarily done by first immersing the individual conductors into a hardenable varnish or resinous plastic, such as Bakelite, and thereafter baking the entire slot conductor under application of heat and pressure, thus solidifying it to an integral rigid body. When, during the operation of the machine, the above-mentioned glow discharges occur, the nitrogen and oxygen in the air within the interior spaces become chemically dissociated, forming nitrogen oxide and monatomic oxygen. With a simultaneous ingress of water vapor, nitric acid is formed. This acid decomposes the plastic between the individual components of the slot conductor so that the junctions become brittle and can no longer firmly secure the individual components to each other. When the slot conductor is subjected to current loading, the individual conductors oscillate due to electrodynamic forces and become loose. After some time, the surrounding insulating sleeve also deteriorates and becomes brittle due to these oscillations so that eventually an electric breakdown occurs.

For avoiding disadvantages described above, it has already been proposed to insulate the composite slot conductor, not by winding the mica-paper sleeve directly upon the conductor but by interposing a conductor layer which is in electrically conductive connection with the individual component conductors so that an electric field and hence a glow discharge cannot be formed within this conductive layer. Practical experience, however, has

2,705,292 Patented Mar. 29, 1955 shown that such a design has several disadvantages. For instance, a good and uniform contact of the added conductive layer at the inner side of the insulating sleeve is not readily obtainable so that air spaces are apt to incur between the sleeve and the interposed conductive ayer.

It is accordingly the principal object of my invention to avoid the occurrence of glow discharges between the slot conductors of electric machines and the surrounding insulating sleeve in a more reliable and yet easily applicable manner.

To this end, and in accordance with a feature of my invention, I provide between the slot conductor and the insulating sleeve two electrically conductive or semiconductive layers, of which one surrounds the slot conductor and is in intimate adhering contact therewith except at the longitudinal edges of the composite conductor, where it is scraped away to expose the bare metal of the individual conductors, while the second layer is in electrical contact with the scraped metallic edges of the conductor as well as being in intimate adhering contact with the inner wall of the insulating sleeve and in electrical contact with the first layer.

In such a structure there may readily be the possibility of an air space occurring between the two intermediate layers. However, an electric field and hence a glow discharge cannot occur within this space because all points along its inner wall surfaces are at the same electric potential. This potential, moreover, is that of the metallic conductor itself.

Still further objects and advantages of the present invention will appear from the more detailed description set forth below, it being understood that this description is given by way of illustration and explanation only, and that various changes may be made by those skilled in the art without departing from the scope and spirit of the appended claims.

In the drawings- Fig. l is a cross-sectional view of the insulated conductor embodying the invention, taken along the line II of Fig. 2.

Fig. 2 is a perspective view of the conductor with sectiOlS broken away to illustrate details of construction, an

Fig. 3 is a cross-sectional view of the conductor illustrating the manner in which the end of the mica paper strip is attached to the conductor assembly prior to its being wound on to produce the insulating sleeve.

As illustrated in Fig. 1 of the drawing, the individual rectangular conductors 1 of the conductor rod are firmly and rigidly joined with each other with the aid of intermediate layers 5 of Bakelite or other thermosetting plastic material; and the outer surfaces of the composite slot conductor are surrounded by a conductive or semi-conductive layer 6 which is in adhering contact with the outer surface of the composite conductor except at the longitudinal edges thereof where it is scraped away to expose the bare metal of the individual conductors 1. A second conductive or semi-conductive layer 7 is disposed upon the inner wall of an insulating sleeve 2 and is in intimate adhering contact with all points of this inner wall. The conductive layer 7 is in electrical contact with each of the individual conductors 1 where it bears against the scraped-away corners along the twisted section (see Fig. 2), thus being maintained at the same potential as the conductor. The conductive layer 7, moreover, overlaps the remaining portions of the layer 6, especially near the edges, so that'electrical contact be tween the two conductive layers 6 and 7 is assured. Complete absence of electric fields in the intermediate air spaces 3 and 4 is thereby achieved. The size of the air spaces 3 and 4 is exaggerated in Fig. l.

The conductive or semi-conductive layers 6 and 7 can be produced in various ways. For instance, a conductive or semi-conductive paint or varnish can be spread upon the slot conductor and upon the inner side of the insulating sleeve. According to an alternative process, a sheet of paper or woven fabric may be used as a carrier for the conductive or semi-conductive layer. To this end, the paper or fabric is painted or otherwise coated with the conductive layer material or is impregnated with a conductive or semi-conductive substance. Suitable as material for the conductive or sem1-conduct1ve layers are,

particularly, carbon'or graphite powder, silicon-carbide 4 powder, or a metal powder. The use of a graphite-containing paper as the conductive layer, the graphite powder being introduced into the paper fibers during the manufacture of the paper, has been found to be especially practicable and effective.

In manufacturing the slot conductor, the following method has been found to be effective.

After the individually insulated conductors 1 are joined together in the usual manner to form the conductor rod, the composite rod is immersed in a resinous thermosetting plastic varnish such as Bakelite.

As is well known, in the slot-traversing portion of a composite conductor rod of the type being described, the individual conductors 1 on the narrow sides of the rectangular cross section change their position from one to the other side of the rectangle. This results in the formation of indentations at the rod surfaces (see Fig. 2). To eliminate resultant air spaces between the surrounding graphite paper and the rod because of these indentations, a conductive putty 8 or other conductive compound, such as graphite putty, is preferably smoothed on to produce an even surface on the narrow sides. A layer of graphite paper 6 is then wound upon the rod so as to envelope the rod on all sides. The graphite paper is conductive on both sides and adheres to the plastic varnish. The plastic varnish is then cured or hardened in a press under application of heat and pressure. During this operation, the graphite paper 6 is tightly pressed against the composite rod so that an intimate adhering junction between the paper and the rod is achieved with the exclusion of any intermediate air spaces. The hardened composite rod is then filed or scraped along the corners to form rounded edges exposing bare metallic surface portions of the individual conductors. During this process, the corner portions of the conductive layer 6 as well as portions of the plastic insulating material 5 are removed. Because of the twisted arrangement of the conductors 1 in the slottraversing section, portions of each individual conductor are thus exposed for electrical contact with the outer conductive layer 7. The outer layer of graphite paper 7 is next wound upon the scraped rod conductor. This outer layer of graphite paper has its conductive surface in electrical contact with the bare metallic edges of the individual conductors 1 as well as with the outer surfaces of the inner layer of graphite paper 6 adhering to the rod. The outer side of the outer layer of graphite paper is varnished. The graphite paper is wound up so that an end strip remains unwound.

In Fig. 3, the conductor rod already surrounded by the inner layer of graphite paper 6 is shown. Wound around the unit is the layer 7 of outer graphite paper. The end strip of the outer layer is denoted by 9. When this stage is reached, a strip of mica paper (mica foil) is attached to the end 9 of the graphite paper by means of shellac, for instance. Thereafter, the mica foil is continuously wound around the conductor until an insulating sleeve of desired wall thickness is produced. The rod is then placed into a heated roller press (rotary ironer) in which the mica foil is solidified to a rigid sleeve under application of heat and pressure, due to the hardening of the shellac. Since the graphite paper located at the inner surface of the insulating sleeve has a varnish coating on its outer side, the just-mentioned processing in the ironer causes the graphite paper to firmly adhere to the inner wall of the insulating sleeve. The occurrence of air spaces between the insulating sleeve and the outer layer of graphite paper is thereby avoided.

The invention also affords the advantage that the difference in thermal coelficient of expansion between the slot conductor and the insulating sleeve will not have a detrimental effect upon the insulating sleeve for the reason that the two conductive layers readily permit an axial displacement between slot conductor and insulating sleeve.

I claim:

1. A slot conductor for dynamoelectric machines, comprising a central, elongated current-conductive member, a first electrically conductive layer means substantially surrounding said conductive member in intimate adhering engagement with the outer surface thereof, a second electrically conductive layer member surrounding said first layer means and in electrical contact therewith and with 'said current-conductive member, and an insulating sleeve surrounding said second layer member, the outer surface of said second layer member and the inner surface of said insulating sleeve being in adhering engagement with each other.

2. A' slot conductor for dynamoelectric machines, comprising a central, elongated current-conductive member, said member consisting of a plurality of individual conductors and insulating intermediate substance firmly joining said conductors with each other, two layers having electric conductance at least of semi-conductive magnitude, a first one of said layers substantially enveloping said member in adhering contact with the outer surface of said member, the second layer enveloping said first layer and being in electrical contact therewith and with said member, and an insulating sleeve enveloping said second layer, the outer surface of said second layer and the inner surface of said insulating sleeve being in adhering engagement with each other.

3. A slot conductor for dynamoelectric machines, comprising a central, elongated current-conductive member, said member consisting of a plurality of individual conductors firmly joined with one another, two electrically conductive layers of which at least one consists essentially of a coating of conductive paint, a first one of said layers substantially enveloping said member in adhering contact with the outer surface of said member, the second layer enveloping said first layer and being in electrical contact therewith and with said member, and an insulating sleeve enveloping said second layer, the outer surface of said second layer and the inner surface of said insulating sleeve being adheringly secured to each other in continuous engagement.

4. A slot conductor for dynamoelectric machines, comprising a central, elongated current-conductive member, said member consisting of a plurality of individual conductors firmly joined with one another, two layers having electric conductance at least of semi-conductive magnitude, at least one of said layers consisting of insulating fibrous material and a conductive impregnation in said material, a first one of said layers substantially enveloping said member in adhering contact with the outer surface of said member, the second layer enveloping said first layer and being in electrical contact therewith and with said member, and an insulating sleeve enveloping said second layer, the outer surface of said second layer and the inner surface of said insulating slefieve being in intimate area engagement with each ot er.

5. A slot conductor for dynamoelectric machines, comprising a central, elongated current-conductive member, said member consisting of a plurality of individual conductors firmly joined with one another, two layers having electric conductance at least of semi-conductive magnitude, at least one of said layers consisting of an insulating carrier and carbon substance on said carrier, a first one of said layers substantially enveloping said member in adhering contact with the outer surface of said member, the second layer enveloping said first layer and being in electrical contact therewith and with said member, and an insulating sleeve enveloping said second layer, the outer surface of said second layer and the inner surface of said insulating sleeve being in intimate area engagement with each other.

6. A slot conductor for dynamoelectric machines, comprising a central, elongated current-conductive member, said member consisting of a plurality of individual conductors firmly joined with one another, two layers having electric conductance at least of semi-conductive magnitude, at least one of said layers consisting of paper impregnated with graphite, a first one of said layers substantially enveloping said member in adhering contact with the outer surface of said member, the second layer enveloping said first layer and being in electrical contact therewith and with said member, and an insulating sleeve enveloping said second layer, the outer surface of said second layer and the inner surface of said insulating sleeve being in intimate area engagement with each other.

7. A slot conductor for dynamoelectric machines, comprising a central, elongated current-conductive member, said member consisting of a plurality of individual conductors firmly joined with one another, two layers having electric conductance at least of semi-conductive magnitude, at least one of said layers consisting of an insulating carrier having a coating of conductive material, a first one of said layers substantially enveloping said member in adhering contact with the outer surface of said member, the second layer enveloping said first layer and being in electrical contact therewith and with said member, and an insulating sleeve enveloping said second layer, the outer surface of said second layer and the inner surface of said insulating sleeve being in intimate area engagement with each other.

8. A slot conductor for dynamoelectric machines, comprising a central, elongated current-conductive member, a layer of electrically conductive paint substantially surrounding said conductive member, an electrically conductive layer member surrounding said coat of paint and in electrical contact therewith and with said member, and an insulating sleeve surrounding said layer member, the outer surface of said layer member and 20 the inner surface of said insulating sleeve being secured to one another in continuous engagement.

9. A slot conductor for dynamoelectric machines, comprising a central, elongated current-conductive member having a plurality of individual conductors, a layer of conductive putty disposed on said member to smooth the surface of said member, a first electrically conductive layer substantially surrounding said smoothed conductive member and secured in adhering contact against the outer surface thereof, a second electrically conductive layer surrounding said first layer and in electrical contact therewith and with said member, and an insulating sleeve surrounding said second layer, the outer surface of said second layer and the inner surface of said insulating sleeve being secured to one another in continuous engagement.

References Cited in the file of this patent FOREIGN PATENTS 369,181 Great Britain Sept. 8, 1930 

